Epitel kanserlerinde WNT/beta-catenin yolağının aktivasyonu

Wnt signaling is involved in a large set of cellular and developmentalprocesses, and when mis-regulated can lead to both degenerative diseases and manytypes of cancer. The involvement of Wnt signaling was already well demonstrated inseveral types of human cancers such as colorectal cancer. However, in some otherssuch as hepatocellular carcinoma (HCC) and breast cancer, the role of Wnt signalingis not fully understood.To study the role of Wnt pathway in liver cancer, we first classified humanhepatoma cell lines into well-differentiated and poorly differentiated groups usinghepatocyte-specific biomarkers. Wnt/β-catenin signaling activity was measuredusing TCF/LEF-dependent reporter assay. Canonical Wnt/β-catenin signaling wasconstitutively active in 80% of well differentiated and 14% of poorly differentiatedcell lines, respectively. Furthermore, ectopic expression mutant of S33Y β-cateninresulted in strong canonical Wnt/β-catenin activity in well differentiated, but not inpoorly differentiated HCC cells. Comprehensive analysis of major Wnt signalingcomponents by a rapid RT-PCR assay showed redundant expression of many Wntligands, Frizzled receptors, co-receptors and TCF/LEF factors in HCC. In contrast,canonical signaling-inhibitory Wnt5A and Wnt5B ligands were selectively expressedin poorly differentiated HCC cell lines. Our observations indicate that canonicalWnt/β-catenin signaling is active in well differentiated, but repressed in poorlydifferentiated HCC cells. Thus, canonical Wnt/β-catenin signaling plays a dual rolein HCC.iiiTo study the role of Wnt pathway in breast cancer, we performed acomprehensive expression analysis, by RT-PCR, of Wnt signaling molecules,including 19 Wnt ligands, ten Frizzled receptors, two LRP co-receptors and fourLef/TCF transcription factors in immortalized normal human mammary epithelialcells (HMECs), six breast cancer cell lines (BCCL) and 14 primary breast tumors(PBT). BCCL expressed/over-expressed all Frizzleds except FZD10, LRP5/6 andLef/TCFs. They also overexpressed WNT4, WNT7B, WNT8B, WNT9A and WNT10B,but the expression of WNT1, WNT2B, WNT3, WNT5A, WNT5B and WNT16 was lostor decreased in most BCCL. Wnt expression correlated with nuclear β-cateninaccumulation and cyclin D1 induction in BCCL, compared to HMECs, indicating areactivation of the canonical Wnt signaling in malignant cells. Furthermore, theexpression of FZD1, WNT-4, WNT7B, WNT8B, WNT9A and WNT10B, all implicatedin canonical Wnt signaling, was upregulated in PBT, whereas the non-canonicalWNT5A expression was down-regulated.Our study gave strong evidences for the differential involvement of Wntpathway in liver and breast cancers. In liver cancer, Wnt pathway activity seems tobe linked to the differentiation status of HCC cell lines. Furthermore, our datashowed that the canonical Wnt pathway was active in well-differentiated HCC celllines and repressed in poorly differentiated ones. In contrast, the study of Wntpathway in breast cancer cell lines showed similarities rather than differences.Indeed, our study revealed a significant correlation between Wnt ligands mRNAexpression profile and the induction of Cyclin D and nuclear β-catenin proteinaccumulation in all breast cancer cell lines studied. We concluded that, althoughinvolved in both types of cancers, Wnt signaling is acting differently in liver andbreast cancers. More interestingly, in the same type of cancer such as HCC, Wntsignaling displayed differential activity depending on the cell differentiation status.iv